Rubber compositions used for tires are desired which provide a balanced improvement in handling stability, fuel economy, durability, ride quality, and adhesion to tire cords.
A proposed method for improving these properties is, for example, to add a modified resorcinol resin or the like to reinforce a rubber matrix. The problems with this method, however, are that it is difficult to increase E* and that the elongation at break is decreased. Thus, this method is unlikely to achieve a satisfactory property balance.
Another proposed method is blending natural rubber having excellent tensile properties at break with a synthetic rubber such as a modified butadiene rubber or a butadiene rubber containing 1,2-syndiotactic polybutadiene crystals. With this method, the elongation at break and the adhesion to cords may be reduced if the dispersibility of polymers is poor. Particularly in the case of a breaker topping rubber, which is required to have safety and perfect durability, there may be some problems with these properties if the synthetic rubber has been scorched or contaminated with a low molecular weight component.
Moreover, Patent Literature 1 teaches a method of using a phenol resin and the like. This method achieves good handling stability, but is not likely to give sufficient ride quality. This method also leaves something to be desired in terms of the adhesion to steel cords, and the like. Thus, there still remains room for improvement in terms of achieving a balanced improvement in handling stability, fuel economy, durability, ride quality, and adhesion.